1. Field of Invention
This invention relates to a replenisher for a xerographic device and a method of replenishing a xerographic device.
2. Description of Related Art
The electrostatographic process, and particularly the xerographic process, is well known. This process involves the formation of an electrostatic latent image on a photoreceptor, followed by development of the image with a developer, and subsequent transfer of the image to a suitable substrate.
Numerous different types of xerographic imaging processes are known wherein, for example, insulative developer particles or conductive developer particles are selected depending on the development systems used. Moreover, of importance with respect to the aforementioned developer compositions is the appropriate triboelectric charging values associated therewith, as it is these values that enable continued formation of developed images of high quality and excellent resolution. In two component developer compositions, carrier particles are used in charging the toner particles.
Carrier particles in part consist of a roughly spherical core, often referred to as the xe2x80x9ccarrier core,xe2x80x9d which may be made from a variety of materials. The core is optionally coated with a resin. This resin may be made from a polymer or copolymer. The resin may optionally have conductive material or charge enhancing additives incorporated into it to provide the carrier particles with more desirable and consistent triboelectric properties.
A problem often encountered with xerographic devices resides in fluctuating triboelectric charging characteristics, particularly over extended use. For example, a developer may start with a certain triboelectric value, and after extended use, the developer may have a significantly lower triboelectric value. This variation in the triboelectric value may result in poor copy quality.
It is known in the art to add additional toner and/or carrier materials to the housing of a xerographic device in order to replenish the materials depleted by the copying (image formation) process of the electrophotographic device. See, for example, U.S. Pat. No. 4,614,165, incorporated herein by reference in its entirety.
In U.S. Pat. No. 4,331,756 to Mayer et al., an electrophotographic developer composition containing a mixture of carrier, toner and zinc stearate as a lubricating additive is described. Mayer describes that it is not possible to completely coat the carrier with zinc stearate since the abrasive action of the constantly moving developer continuously removes the zinc stearate. The zinc stearate is added directly to the developer as a separate component. The zinc stearate is also used as an additive to the toner.
In U.S. Pat. No. 5,171,653 to Jugle et al., a developer composition is described which consists essentially of a toner consisting essentially of a resin, a colorant, a charge control agent, and colloidal silica external additive particles and a carrier consisting essentially of a core, an optional coating on the core, and an external additive selected from the group consisting of metal salts of fatty acids, linear polymeric alcohols comprising a fully saturated hydrocarbon backbone with at least about 80 percent of the polymeric chains terminated at one chain end with a hydroxyl group, polyethylene waxes with a molecular weight of from about 300 to about 2,000, polypropylene waxes with a molecular weight of from about 300 to about 3,000, and mixtures thereof. The metal salt of fatty acids may be zinc stearate. A method of adding a replenisher with a higher triboelectric value than the developer to which the replenisher is added is not disclosed, nor is a method of adding a replenisher containing a zinc stearate coated carrier with a higher triboelectric value than the developer to which the replenisher is added disclosed.
The addition of additional fresh toner and/or carrier will enable the user to maintain preferred triboelectric values in the electrophotographic device. However, this is an expensive method to maintain the triboelectric value since the xerographic device will use extra toner and/or carrier. Further, the addition of fresh toner and/or carrier results in increased amounts of waste in the sump of the xerographic device.
What is desired is a better method of maintaining the triboelectric value of developer by adding an improved replenisher that requires less of the replenisher.
What is desired is a replenisher that maintains the triboelectric properties of a xerographic device over an extended period of use.
It is an object of the present invention to provide a replenisher for a xerographic device that maintains the triboelectric properties over an extended period of use of the xerographic device.
It is a further object of the present invention to provide a replenisher that produces less waste.
It is a still further object of the present invention to provide a method of replenishing the developer that is economical.
These and other objects of the present invention are achieved by providing a replenisher comprising carrier particles coated with zinc stearate. The zinc stearate coated carrier particles may have a higher triboelectric value than the carrier originally present in the developer.